1. Field of the Invention
Embodiments described herein generally relate to a scintillator, a scintillator array, a radiation detector, and a radiation inspection device.
2. Description of Related Art
Radiation inspection devices such as an X-ray CT (Computed Tomography: CT) device have been used for various fields including medical use, industrial use, or the like. For example, there is disclosed a multi-slice X-ray CT device provided with a scintillator array which has detection elements (photodiodes or the like) vertically and horizontally arranged in two dimensions. Employment of a multi-slice type makes it possible to superpose cross-sectional images, whereby three-dimensionally expressing the CT image is enabled. A radiation detector mounted on the radiation inspection device includes a plurality of detection elements arranged vertical and horizontal lines. Each of the plurality of detection elements is provided with a scintillator. In other words, one scintillator is provided in one detection element.
An X-ray incident on the scintillator is converted into visible light, and the visible light is converted into an electric signal by the detection element and output as an image. In recent years, in order to obtain high resolution, the detection element is downsized and a pitch between adjacent detection elements is reduced. Accompanying the above, a size of the scintillator is also reduced to 1 mm3 or less in volume.
As for a material of the scintillator, for example, a ceramic scintillator made of a gadolinium oxysulfide sintered body can be cited. A body color of the ceramic scintillator indicates certain chromaticity coordinates (x, y). The chromaticity coordinates are measured by using a color meter. A minimum measurement range of a general color meter is about 2 to 8 mm in diameter. A measurement area of the measurement range when a diameter is 2 to 8 mm, for example, is 3.14 to 50.24 mm2. The chromaticity is regarded as appropriate even when a minute discoloration region of less than about 1 mm2 in area exists in the above range. The discoloration region means a discoloration region existing in one ceramic scintillator.
In a case where the ceramic scintillator is small in size, influence on emission characteristics due to comparatively minute discoloration region becomes large when the minute discoloration region exists. That is, if the minute discoloration region is generated, an optical output at the time that the X-ray is converted into visible light is reduced. In particular, in the scintillator array having a plurality of ceramic scintillators arranged vertically and horizontally in two dimensions, when the optical output of the ceramic scintillator partly decreases, sensitivity variation of the scintillator array becomes large. The ceramic scintillator is manufactured by being cut out of an ingot being a large sintered body. When the minute discoloration region exists in the ingot, the optical output of each ceramic scintillator is reduced, resulting in sensitivity variation of the scintillator array.